Computer Drive and its method of forcing the transistors in the
hybrid to remain turned on to some degree at all times seems
to make them run really HOT. Every SA-310 and 410 I've ever
seen gets very hot, especially when idling. I'm going to install
a fan. The heatsink becomes ridiculously hot after ten minutes
of operation, so hot it can't be touched. I don't think this can
be good for the hybrid.

Some years ago an audiophile reviewer complained that an amplifier's
heatsinks got unduly hot. The manufacturer replied that that was the purpose
of the heatsink, to remove heat from the output stage.

Although this makes a sort of sense, the fact is that an extremely hot
heatsink -- except when the amplifier is driven to the point of maximum
dissipation, which I believe is about 35% of clipping power for a weakly
biased class-AB amp -- suggests that the heatsink isn't big enough.